The present invention relates to an image forming apparatus, an image forming method and a computer-readable storage medium having an image forming program. More particularly, the present invention relates to a portable and simple image measuring technology utilized for surveying and making a drawing in a land surveying field, which uses digital processing by digital photogrammetry and a personal computer.
Specifically, the present invention relates to an image forming technology for forming a digital orthogonally projected image (ortho-image) from one to a plurality of images to be superposed on the drawing when a drawing of a site to be measured is made. The present invention relates to an image forming technology which enables any operator to easily make a drawing of an orthogonally projected image by using a survey instrument and images so as to stick an ortho-image to the drawing, and also enables a digital orthogonally projected image to be generated and rectified such that the situation of a site to be measured can be understood in detail. An object of the present invention is to provide an image which enables stable stereo analysis to be performed even for a stereo-image.
The present invention can also be applied to, for example, an image obtained by photographing a wide range divided into small images having overlapping areas with one another.
According to a prior art, a drawing obtained by surveying in a site to be measured has been made by using paper and a pencil or the like which are typically used in plane table surveying. In recent years, a line drawing of a site to be measured has been made by using a survey instrument and a portable computer in combination which are typically used in pen-based mapping system.
FIG. 18 is a view illustrating conventional stereo-image measuring. Usually, as shown in the drawing, the three-dimensional coordinates are obtained by photographing two or more overlapped images based on the principle of triangulation by stereo-image photographing. If a target range is wide, a plurality of images are photographed. For example, in even a simple site, photographing of ten to twenty images is usually necessary. In this case, unless orientation (i.e., calculating a camera position, inclination or the like) can be performed for each stereo pair (model), a stereo-image cannot be rectified. Three-dimensional measuring cannot be performed, either.
In the conventional case, however, a drawing was expressed only by a line image even if it was made in the actual place, and it was impossible to sufficiently understand the situation of the site. Thus, the situation of the site was photographed by a camera. However, since photographing was performed from an oblique direction whereas a direction of a requested drawing was vertical, a photographed image had no direct connection with the drawing. As a result, it was necessary for an operator to understand the situation of the site by comparing the drawing with the image. This practice was inconvenient, and understanding of the site was difficult.
A range to be photographed with one image was limited. Even in the case of photographing a plurality of images, because correlation and continuity among the respective photographs are lacking, this led to the difficulty of obtaining consistency among the photographs, and comparison with the drawing was complicated and difficult. If a highly accurate ortho-image was required, lens distortion of the camera was an obstacle. Conventionally, it was impossible to produce a highly accurate ortho-image by a camera which has no data on lens distortion.
In the case of conventional land surveying, for surveying a site to be photographed and making a drawing for the site, it was necessary to survey an enormous number of points and perform three-dimensional measuring. Thus, much man power and labor had to be expended. On the other hand, if a close and terrestrial photogrammetry is used, indirect survey three-dimensional data can be obtained only by photographing. But since only a camera using a film was available conventionally, developing and scanning took time (e.g., two to three days), and several days were also expended for analyzing work. Unless processing up to analysis was carried out after film development, there was no knowing whether photographed image data was analyzable or not, and whether stable, sure and highly reliable analysis was possible or not. As a result, conventionally, this method has not been used so often because the necessity to again perform the work such as photographing may happen.
With popularized and increased use of digital cameras in recent years, digital close and terrestrial photogrammetry can now be performed by a digital camera which is different from a conventional film or analog camera. Use of this technology eliminates labor and time for film development and scanning. Since analysis is performed by a computer, the process from photographing to analyzing can be finished within one to two days.
However, after acquisition of photographic data, it was necessary to bring the photographic data to the place of an analyzing device (computer) for analysis and measuring. Thus, photographing improper for analysis might result in the necessity to again perform the work such as photographing, and stable and sure analysis was not always carried out.
For performing analysis and measuring by images, if control point/orienting point arrangement, a photographic range, photographic overlapping or the like was not proper, stable and highly reliable analysis was impossible. Consequently, unstable results occurred, and even analysis itself was impossible.
The present invention was made with the foregoing points in mind. The object of the present invention is to provide an image forming apparatus for, when a drawing of the situation of a site to be measured is made, easily making a drawing of the site from an orthogonally projected image (ortho-image) so as to facilitate understanding of the situation. The object of the present invention is to quickly and easily generate/rectify an image in the site to be measured without any storage omission or mistakes, to understand the situation of the site on the spot, and to easily make an image drawing (ortho-image) in real time while confirming the same. The object of the present invention is to perform image complementary measuring only by simple photographing and surveying of several points with a survey instrument, to simultaneously obtain an image drawing for facilitating understanding of the situation of the site, to interpolate portions not photographed or hard to make out, and to produce an ortho-image of a high resolution and wide range.
Another object of the present invention is to facilitate understanding of a situation from a plurality of images, even if the situation is hard to grasp, for example, some parts are difficult to see or a far part becomes rough with one image, and produce a highly accurate ortho-image. The object of the present invention is to integrate a plurality of images by repeating simple work and obtain a wide-ranging ortho-image. Further, the object of the present invention is to form a highly accurate and high-quality ortho-image at a high speed by photographing a plurality of images overlapped with adjacent areas.
The still another object of the present invention is to correct lens distortion (camera calibration correction) by simple measuring, and simultaneously form a highly accurate ortho-image even by a camera having no lens distortion data. Further, the object of the present invention is to form a good quality ortho-image of a necessary place with required accuracy by using various survey instruments to rectify the ortho-image while measuring the three-dimensional coordinates.
According to the present invention, the following operations and confirmation can be performed in a site to be photographed:
(1) confirmation of a measuring range (e.g., overlapping);
(2) generation and confirmation of an ortho-image obtained by integrating plurality of images;
(3) confirmation of the entire measuring/photographing range and a range to be drawn.
(4) confirmation of entire arrangement of control points/orienting points; and
(5) confirmation of orientation, and confirmation of a model formed for stereo method analysis.
In accordance with first solving means of the present invention, there is provided an image forming apparatus, which comprises:
a control point measuring section for measuring a centrally projected image having a plurality of control points, and obtaining the image coordinates for said control points;
a coordinate transformation parameter calculating section for obtaining a transformation parameter for correlating, based on said image coordinates for said control points obtained by said control point measuring section and the three-dimensional coordinates for actually measured control points, said image coordinates with said three-dimensional coordinates;
an orthogonally projected image (ortho-image) forming section for forming an orthogonally projected image from said centrally projected image based on said transformation parameter obtained by said coordinate transformation parameter calculating section; and
an ortho-image correcting section for correcting the image coordinates obtained by said ortho-image forming section based on the three-dimensional coordinates for actually measured additional points, and then performing correction of said orthogonally projected image.
In accordance with second solving means of the present invention, there are provided an image forming method, an image forming apparatus and a computer-readable storage medium having an image forming program. In this case, the image forming method comprises:
an image input function, to which a plurality of images including control points or orienting points overlapped with one another are inputted;
a storage function for previously storing ground coordinate values of control points or orienting points;
an orthogonally projected image (ortho-image) forming function for forming an ortho-image from plurality of images inputted by said image input function based on image coordinate values, alternatively photographic coordinate value, and said ground coordinate values of the control points or the orienting points; and
a determining function for determining, based on the ortho-image formed by said ortho-image forming function, necessity of re-photographing, and necessity of changing a photographing position, alternatively a control point or an orienting point position.